ZOOMASTIGINA, RHIZOMASTIGINA 



337 



zoites voided in faeces by infected birds may become the source of 

 new infection when taken in by young birds with drink or food. 

 Tyzzer (1920) found the organism to possess a flagellate stage and 

 established the genus Histomonas for it. Tyzzer and Fabyan (1922) 

 and Tyzzer (1934) demonstrated that the organism is transmissible 

 from bird to bird in the eggs of the nematode Heterakis gallinae, 

 which method appears to be a convenient and reliable one for pro- 

 ducing Histomonas infection in turkeys (McKay and Morehouse, 



Fig. 137. Histomonas meleagridis. a-d, from host animals (Wenrich); 

 e-h, from cultures (Bishop), a, b, organisms in caecum of chicken (in a 

 Tyzzer slide); c, an individual from pheasant showing "ingestion tube" 

 with a bacterial rod; d, a large individual from the same source, all 

 X1765; e, an amoeboid form; f, a rounded form with axostyle (?); g, h, 

 stages in nuclear division, X2200. 



1948). Desowitz (1950) noticed in a Heterakis two enlarged gut cells 

 filled with amoebulae which he suggested might be a stage of this 

 protozoan. Niimi (1937) reported that the organism enters through 

 the mouth of the nematode and invades its eggs. Dobell (1940) points 

 out the similarity between this flagellate and Dientamoeba fragilis 

 (p. 462). Wenrich (1943) made a comparative study of forms found in 



